1. Field of the Invention
The present invention relates to a method for producing a non-graphitizable carbon material, a negative electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.
2. Discussion of the Background
Nowadays, since there is growing worldwide awareness of global environment conservation issues, hybrid vehicles (HEV, PHEV) and electric vehicles (EV), which are effective for realizing the reduction of the amount of fossil fuels used and CO2 emission, are receiving a lot of attention. There is a trend toward the research and development of lithium ion secondary batteries (LIB), which have a high energy density per volume and mass, and which can be easily reduced in size, for the power sources of hybrid vehicles and electric vehicles. Carbon materials are generally used as negative electrode materials of lithium ion secondary batteries. Other than carbon materials, for example, lithium salts of the metal or metal oxide of, for example, Si, Sn, Ti, or V and hybrid materials of carbon and metal, which have a high energy density, are currently in the research stage.
Among carbon materials, graphite-based materials have been widely used for, for example, mobile electronic devices because these materials have high capacity. Non-graphitizable carbon, which has high input-output performance and cycle performance, is receiving a lot of attention as a negative electrode material of on vehicle batteries. In particular, since batteries for hybrid vehicles are required to have high input-output performance, which is necessary to start a vehicle and to collect regenerated energy, and a life span property, with which it is possible to repeat charge and discharge cycles over a long time, non-graphitizable carbon materials are suitable for the negative electrode materials of the batteries of hybrid vehicles.
Regarding non-graphitizable materials as negative electrode materials of lithium ion secondary batteries, materials made from petroleum pitches or coal pitches have been disclosed (refer to, for example, Japanese Unexamined Patent Application Publication No. 3-252053, Japanese Unexamined Patent Application Publication No. 6-89721, Japanese Unexamined Patent Application Publication No. 8-115723, and Japanese Unexamined Patent Application Publication No. 9-153359).